1. Field of the Invention
The present invention relates generally to a transceiver module, and in particular, to a bi-directional optical transceiver module of a planar optical waveguide type for bi-directional optical transmission and reception.
2. Description of the Related Art
A typical bi-directional optical communication system includes a light source for converting an electrical signal to an optical signal and an optical detector for detecting an external input optical signal. However, the bi-directional optical communication system is not effective in terms of cost and size as the light source and the optical detector are separately constituted. Integrating a light source and an optical detector within a bi-directional optical transceiver module has become common as a consequence of the recent development and proliferation of optical communication systems that can perform bi-directional optical communication through a single optical fiber. A substrate may be implemented, for example, by hybrid-integrating a light source and an optical detector on the substrate along with planar waveguides.
FIG. 1 illustrates a conventional bi-directional optical transceiver module having an optical waveguide divided into two branch waveguides and a directional coupler. The module 100 includes a 2-branch waveguide 110, a multilayer thin-film filter 160, a light source 130 for outputting a transmission optical signal λ1, an optical fiber 140 serving as an input/output medium for the transmission optical signal λ1 and a reception optical signal λ2, an optical detector 120 for detecting the reception optical signal λ2, and a waveguide substrate 150.
A lower clad layer (not shown), a core layer (not shown), and an upper clad layer (not shown) have sequentially been deposited on the upper surface of the waveguide substrate 150, to thereby form the 2-branch waveguide 110. The optical fiber 140, the light source 130, and the optical detector 120 are mounted on the waveguide substrate 150.
A non-branched end 111 of the 2-branch waveguide 110 is connected to the optical detector 120, while one branched end 113 of the waveguide 110 is connected to the light source 130 and the other branched end 112, to the optical fiber 140. The multilayer thin-film filter 160 is secured in a groove 151a formed into the upper surface of the waveguide substrate 150, so that it is positioned at the center of the 2-branch waveguide 110.
The multilayer thin-film filter 160 reflects the transmission optical signal λ1 received through the branched waveguide end 113 connected to the light source 130 to the other branched waveguide end 112, and passes the reception optical signal λ2 received from the branched waveguide end 112 to the non-branched waveguide end 111 connected to the optical detector 120.
The conventional bi-directional optical transceiver module suffers great loss in light intensity if the position of the multilayer thin-film filter is less than precisely aligned. Therefore, either the need for precise alignment means for the multilayer thin-film filter increases product cost or light intensity loss reduces the reception sensitivity of the optical detector.
An example of a bi-directional optical transceiver module having a multilayer thin-film filter is found in U.S. Pat. No. 6,480,647 entitled “Waveguide Type Wavelength Multiplexing Optical Transmitter/Receiver Module” to Naoki Kitamura et al (“the '647 patent”). The bi-directional optical transceiver module in the '647 patent minimizes intensity loss of transmission and reception optical signals by use of a multilayer thin-film filter mounted on the upper surface of a waveguide substrate and waveguides that form optical paths connected to the multilayer thin-film filter.
However, this bi-directional optical transceiver module requires means for aligning and supporting the optical detector and the waveguide substrate, thereby increasing product cost.
An exemplary bi-direction optical transceiver module with a 2-branch optical waveguide and a non-branched optical waveguide is disclosed in U.S. Pat. No. 5,825,951 entitled “Optical Transmitter-Receiver Module” to Naoki Kitamura et. al. (“the '951 patent”). A reception optical signal input to a non-branched end of the 2-branch waveguide is branched and then transmitted to an optical detector. A transmission optical signal input to the turning optical waveguide is mode-coupled to a branched end of the 2-branch waveguide and transmitted through an optical fiber.
A shortcoming of this bi-directional optical transceiver module, however, is great loss in the intensity of transmission and reception optical signals due to the use of the 2-branch waveguide.